Method for providing a curved cooling channel in a gas turbine component as well as coolable blade for a gas turbine component

ABSTRACT

Method for providing a curved cooling channel ( 20 ) into a gas turbine component, in particular into a blade ( 10 ), by means of an electrode ( 2 ), wherein an electrode ( 2 ) in the form of a helix is used, and the electrode ( 2 ) is driven so as to rotate around its central rotational axis (R); as well as coolable blade ( 10 ) for a gas turbine component with a helical cooling channel ( 20 ).

FIELD OF TECHNOLOGY

[0001] The invention relates to a method for providing a curved cooling channel in a gas turbine component according to the preamble of claim 1. The invention furthermore relates to a coolable blade for a gas turbine component according to the preamble of claim 3.

STATE OF THE ART

[0002] In general, cooling channels in gas turbine components are designed in the form of holes that are placed along a hole axis that extends in a straight line. In a number of applications, such as, for example, gas turbine blades subject to high thermal loads that have a complex geometry, it is difficult to apply cooling channels in a suitable manner to especially highly loaded sections. At hard-to-access points, such as, for example, in the transition area between the blade hub and the platform or in wall sections with high thermal loads, holes whose axis does not extend linearly, but which follow a curve that curves three-dimensionally in space, would have to be provided.

[0003] EP 0 659 978 A1, on which this invention is based, discloses a coolable turbine blade that is constructed in the manner known per se of a blade hub, a blade root, and a platform. The blade hub consists of a suction-side and a pressure-side wall that are connected with each other via a leading edge and a trailing edge while forming a cavity. Curved channels are provided in the region of the blade tip.

[0004] With respect to providing the curved channels, this document very generally refers to electrochemical processes and also laser beam drilling. However, this document does not provide further details related to this.

[0005] It is further noted that the curved channels shown there have been positioned in the region of the blade tip. Starting from the pressure side of the blade, they extend to the blade tip. This means that it is an area that is easily accessible, and therefore permits the providing of a curved channel without greater difficulties. Difficulties are encountered, however, when this technology is transferred to the initially described, hard-to-access areas of a gas turbine blade.

DESCRIPTION OF THE INVENTION

[0006] The invention attempts to avoid the described disadvantages. It is based on the one hand on the objective of making available, by means of an electrode, a method for providing a curved cooling channel into a gas turbine component, in particular into a blade, said method making it possible to provide cooling channels even at hard-to-access places. On the other hand, the invention is based on the further objective to design a coolable blade for a gas turbine component, in particular a turbine blade, that is provided with a curved cooling channel that enables the required heat removal even at hard-to-access places.

[0007] According to the invention, this is achieved in a method in that an electrode in the form of a helix is used. The electrode is driven so as to rotate around its central rotational axis, resulting in a curved channel in a helical shape. This makes it possible to provide in a simple manner cooling channels in areas subjected to high thermal loads, especially at the transition areas between platform and blade hub or in the wall of the blade hub.

[0008] Naturally, the electrode must be positioned axially movable in relation to the rotational axis so as to permit the corresponding advance according to the pitch of the helix.

[0009] It is preferred that the electrode is driven in a forcibly coupled manner, axially movable in relation to the rotational axis. This ensures that the electrode is guided optimally in the respective channel section that was just created.

[0010] With respect to the selection of the cross-section shape of the electrode wire, i.e., the cross-section shape of the created cooling channel, there is substantial freedom. In addition to rectangular cross-sections, in particular circular or ellipsoid cross-section can be realized in order to ensure optimum flow conditions within the cooling channel.

[0011] Even though the method described above can be used in practically all gas turbine components, it is used preferably in coolable blades.

[0012] The initially described objective is realized in a coolable blade according to the class in that the cooling channel has at least one section with a helical shape. Such cooling channels enable an extremely efficient cooling especially of those places that are subject to especially strong thermal stresses. Even hard-to-access places, such as the transition area from blade hub to platform or wall areas of the blade hub that are subject to especially high loads due to hot gas can be cooled optimally.

[0013] A first group of preferred embodiments of such a blade relate to the cooling channels provided in the wall of the blade hub.

[0014] A first version provides that the cooling channel extends substantially continuously over the entire height of the blade hub. This means that the blade hub is cooled for the most part evenly in the direction of the blade height. Such a cooling channel also can be produced economically since it can be drilled in a single working step.

[0015] Depending on the thermal load introduced by the hot gas flow, it may be advantageous that several cooling channels that are separate from each other are provided.

[0016] It was found to be advantageous, for example, that several laterally juxtaposed cooling channels are provided. In particular in the area of the leading edge, three to five of these cooling channels can be provided in an axis-parallel arrangement, for example, in order to always ensure a safe cooling of the corresponding wall section in case of a potential shifting of the stagnation point.

[0017] Another preferred version provides that the cooling channels are arranged below each other. In this case, the cooling channel does not extend continuously over the entire height of the blade hub, but only over a specific partial section. This makes it possible to account for the thermal load that varies over the blade height, and to provide cooling channels at the places where the thermal load is highest. This configuration also makes it possible to increase the cooling power since the cooling medium is added and removed at several places along the blade height.

[0018] Another version, finally, provides that several cooling channels are stacked inside each other. The radial and/or axial offset of the individual cooling channels is selected so that they all extend separately from each other. This allows a strong cooling effect at places with especially high thermal loads without weakening the cross-section of the wall too much.

[0019] Another interesting aspect is the possibility of providing ejection openings for forming a cooling film. The ejection openings are designed as so-called film holes that start from the cooling channel and end at the surface of the blade hub. A suitable design of the helical extension of the cooling channel makes it possible to achieve an optimum cooling film. This also can be supported by the swirl of the cooling air flow created by the helical shape.

[0020] Another important application finally relates to providing such a cooling channel in the transition area from the blade hub to the platform. This transition area usually has a transition radius that is subject to very large thermal and mechanical loads. This area therefore must be cooled in a targeted manner in order to not exceed the maximum permissible load values.

[0021] It is preferred that the cooling channel is provided with several supply and outlet channels so that the coolant is not excessively heated when flowing through the cooling channel. Such a cooling channel can be created in a simple manner in that during the pacing of the cooling channel, the helical electrode is positioned so that only one angle sector of one turn extends inside the blade, and the remaining sector is located in the area of a cavity through which the coolant flows. This creates several cooling channel sections located on top of each other, which can be supplied optimally by the coolant flowing in the cavity.

BRIEF DESCRIPTION OF DRAWING

[0022] The drawing shows exemplary embodiments of the invention in schematic form. Hereby:

[0023]FIG. 1 shows an x-ray of a blade section with electrode; perspective view;

[0024]FIG. 2 shows a blade section with electrode; perspective view;

[0025]FIG. 3 shows a blade section without electrode; perspective view;

[0026]FIG. 4 shows a blade section with cooling channels according to a first embodiment; sectional view;

[0027]FIG. 5 shows a blade section with cooling channels according to a second embodiment; sectional view;

[0028]FIG. 6 shows a blade section with cooling channels according to a third embodiment;

[0029]FIG. 7 shows a wall section of a blade with cooling channels according to a first embodiment, sectional view; and,

[0030]FIG. 8 shows a wall section of a blade with cooling channels according to a second embodiment, sectional view.

[0031] Only those elements essential for understanding the invention are shown and described.

WAY OF EXECUTING THE INVENTION

[0032] The method according to the invention is explained in particular in reference to the exemplary embodiment shown in FIGS. 1 to 3, said embodiment showing the section of a blade 10 in the transition area from a blade hub 12 to a platform 16. Below the platform 16, a cavity 28 is formed, which is limited on one side by the platform 16, and on the other side by a blade root 14, and whose function is explained in more detail below.

[0033] According to the invention, an electrode in the shape of a helix 2 is used, which is driven here, in a manner not shown in detail, so as to rotate around its rotational axis R. Forcibly coupled with the rotational movement, the electrode 2 is driven axially movable, causing the electrode 2 to advance into the material in the area of the platform 16 and of the blade root 14. For this purpose, a method known per se, such as, for example, a spark erosion method or an electrochemical drilling method, is used.

[0034] The coupled rotational and shifting movement causes the electrode 2 to be driven forward helically. This creates a channel or cooling channel 20 that is constructed helically in the section processed by the electrode 2. If the electrode is positioned completely within, for example, the platform 16, a continuous cooling channel 20 is created.

[0035] In the exemplary embodiment shown here, the electrode 2 is positioned in relation to the platform 16 and the blade root 14 in such a way that, when seen from the top, an angle sector is located in the area of the cavity 28. The electrode 2 therefore exits the blade root 14 in each case, and enters the area of the platform 16 following another rotation of about 90°. This does not create a single, continuous cooling channel 20, but a plurality of parallel extending channel sections with inlet openings 22 and outlet openings 24.

[0036] With respect to the geometric design of the helix 2, there is substantial freedom. Naturally, the pitch of the helix 2 is the determining factor for the axial movement in relation to the rotation. The forcible coupling is actually necessary only at the beginning of the drilling process, since afterwards the helix 2 is guided in the already drilled section. This only applies if the electrode 2 has a sufficient mechanical stability, however.

[0037] The embodiments according to FIGS. 4 to 6 show different possibilities for using such cooling channels in order to realize different cooling concepts in the transition area between the blade hub and platform. Because of the small radius at this point, in connection with the high thermal load, this transition area is especially at risk and therefore must be cooled optimally.

[0038]FIG. 4 shows a blade 10 with a blade hub 12, a blade root 14, and a platform 16. The blade hub 12 is constructed hollow, i.e., a cavity 19 exists between the walls 18, whereby a coolant K can flow through said cavity (not shown here).

[0039] In the transition area between blade hub 12 or blade root 14 and platform 16, a helically extending cooling channel 20 is illustrated. In the area of the blade root 14, an inlet opening 22, and in the area of the platform 16, an outlet opening 24 is provided. Below the platform 16, a baffle plate 30 is positioned so that a cavity 28 is created between the platform 16 and the baffle plate 32 [sic].

[0040] In a manner known per se, the baffle plate 30 has baffle holes 32, through which the coolant K first enters the cavity 28, and from there leaves the blade 10 in the area of the platform 16 through ejection openings in the form of film holes 26.

[0041] A portion of the cooling air flow K furthermore flows through the inlet opening 22 located in the area of the blade root 14 below the baffle plate 28 [sic]. As a result of the pressure differential between this area and the cavity 28, this portion of the cooling air flow K flows through the cooling channel 20, and exits it through the outlet opening 24 in the area of the cavity 28. There, it is mixed with the remaining coolant K and exits the blade 10 through the film holes 26.

[0042] As illustrated in particular in FIG. 3, a plurality of inlet openings 22 and outlet openings 24 are provided, enabling an even cooling along a plane vertical to the drawing plane according to FIG. 4.

[0043]FIGS. 5 and 6 show variations of channels 20 by means of a half-section analog to the illustration in FIG. 4.

[0044] The embodiment according to FIG. 5 has a first group of cooling channels 20 in the transition area between the wall 18 and the platform 16, as well as a second group of cooling channels 20 in the end portion of the platform 16. Both groups of cooling channels 20 are supplied exclusively through the cavity 28.

[0045] The variation according to FIG. 6 shows a helical cooling channel 20 that is continuous vertically to the drawing plane and is supplied by a feeding channel 23 and has a outlet channel 25 that ends in the area of the hollow space 19. It is also possible to provide a plurality of feeding channels 23 and outlet channels 25 in order to even the cooling effect.

[0046] The variations shown in FIG. 7 and 8 show cooling concepts that can be realized within a wall 18 (for example in the stagnation point area of the blade 10). Shown are five cooling channels 20 that extend (not shown) substantially over the entire height of the blade hub 12, i.e., vertical to the illustrated section plane. The arrangement is furthermore selected so that each of the cooling channels 20 extends separately from the others, whereby the laterally and vertically stacked arrangement achieves that an optimized cooling is produced.

[0047] The embodiment shown in FIG. 8 differs from the one in FIG. 4 in that outlet channels 25 have been provided. These enable the formation of a cooling film (not shown in detail).

[0048] Another variation of the embodiments according to FIGS. 7 and 8 provides that the individual cooling channels 20 are provided not continuously over the entire height of the blade hub. Instead, individual helical cooling channels, each having a few turns, are provided so as to be positioned on top of each other, but separate from each other. These can be arranged, for example, specifically more densely in the middle of the blade height in order to account for the local heat introduction through the hot gas flow.

[0049] The concept according to the invention makes it possible to economically realize optimum cooling concepts, in particular to provide even hard-to-access places with cooling channels. List of Reference Numerals  2 electrode, helix 10 blade 12 Blade hub 14 Blade root 16 Platform 18 Wall 19 Cavity 20 Cooling channel 22 Inlet opening 23 Feeding channel 24 Outlet opening 25 Outlet channel 26 Film hole, ejection opening 28 Cavity 30 Baffle plate 32 Baffle hole K Coolant R Rotational axis 

1. Method for providing a curved cooling channel into a gas turbine component, in particular into a blade, by means of an electrode, characterized in that an electrode (2) in the form of a helix is used, and that the electrode (2) is driven so as to rotate around its central rotational axis (R).
 2. Method according to claim 1, characterized in that the electrode (2) is driven in a forcibly coupled manner, axially movable in relation to the rotation axis (R).
 3. Coolable blade for a gas turbine component, in particular a turbine blade, with a blade hub, a blade root, and a platform, as well as at least one curved cooling channel, characterized in that the cooling channel has at least one helical section (20).
 4. Blade according to claim 3, characterized in that the cooling channel (20) is provided in a wall (18) of the blade hub (12).
 5. Blade according to claim 4, characterized in that the cooling channel (20) extends substantially over the entire height of the blade hub (12).
 6. Blade according to claim 4 or 5, characterized in that several cooling channels (20) that are separate from each other are provided.
 7. Blade according to claim 6, characterized in that the cooling channels (20) are positioned laterally next to each other.
 8. Blade according to claim 6, characterized in that the cooling channels (20) are positioned below each other.
 9. Blade according to claim 7 or 8, characterized in that the cooling channels (20) are positioned stacked inside each other.
 10. Blade according to one of claims 4 to 9, characterized in that ejection openings (26) for forming a cooling film are provided, which ejection openings originate from the cooling channels (20).
 11. Blade according to claim 3, characterized in that the cooling channel (20) is provided in the transition area from the blade hub (12) to the platform (16).
 12. Blade according to one of claims 3 to 11, characterized in that the cooling channel (20) is provided with several feeding and/or outlet channels. 